The proposed project, titled HIV Testing & Latino MSM: Individual, Sociocultural and Structural Determinants, aims to determine combinations of individual, sociocultural, and community-level factors that must be targeted within different subgroups of adult Latino gay, bisexual, and other men who have sex with men (LMSM) to maximize efficacy of HIV testing prevention efforts. Many HIV positive LMSM are unaware of their infection. Lack of awareness of HIV serostatus leads to an increased likelihood of HIV transmission and perpetuation of the overall HIV/AIDS heath disparity affecting Latinos in the United States. The overarching goal of this research is to improve participation of LMSM in HIV testing initiatives [e.g., Seek-Test-Treat-Retain (STTR) interventions] by increasing our scientifi understanding of within-LMSM group differences in obtaining HIV testing. The proposed three-year prospective study will (a) use latent class analysis to empirically identify typologies of 415 adult LMSM (aged 18 years and older) based on their individual, sociocultural, and structural- level factors and (b) determine whether and to what extent rates of HIV testing differ by subgroup, while accounting for recognized demographic covariates. Our conceptual model and hypotheses account for well- established individual, social, and cultural determinants of HIV testing. Proposed hypotheses will be tested using data obtained from rigorous Internet-based data collection procedures. Participant recruitment will occur via targeted online social networking groups (e.g., dating and general interest groups) and community-based agencies serving LMSM in upstate New York, New York City, and four other metropolitan areas in which HIV prevalence among Latino males is highest in the United States (Miami, Los Angeles, Chicago, Houston). Our research team, including community based investigators and undergraduate health disparities research fellows, is well-poised to implement the proposed project. The proposed study builds upon the investigators' prior work on individual, sociocultural, and structural determinants of HIV risk and related behaviors among Latinos; HIV prevention and health promotion among sexual minorities; sexual identity development theory; advanced statistical analyses, and longitudinal designs. Findings will have high public health importance because they will inform the next generation of HIV testing campaigns of novel facilitators of HIV testing. Results also will highlight subgroups (based on determinants of testing) of LMSM-an underserved population that is affected by delayed HIV testing and late entry to care.